The present invention relates to a fuel cut control device for an internal combustion engine that controls and cuts fuel during deceleration of a four-cycle internal combustion engine.
In order to improve fuel economy of an internal combustion engine or to clean exhaust gas, fuel cut control is performed to stop supply of fuel during deceleration of the engine.
As described in Japanese Patent Laid-Open Nos. 10-339187 and 2002-213289, a conventional control device having a capability of fuel cut control includes a throttle sensor that detects an opening degree of a throttle valve, and stops supply of fuel when an engine rotates at a higher rotational speed than a predetermined rotational speed in a state where the sensor detects that the throttle valve is closed.
The state where the throttle valve is closed is a state where a load of the engine is low (a deceleration state), and a state where the engine rotates at a high rotational speed though the engine is in the low load state is a state where the engine is rotated by an external force. In this state, the engine does not need to generate an output, and thus fuel cut control can be performed.
Performing the fuel cut control when the engine does not need to generate the output saves fuel consumption, and also reduces the amount of hazardous exhaust gas because unnecessary combustion is avoided.
As described above, the conventional fuel cut control device requires detection of the opening degree of the throttle valve, which requires an expensive throttle sensor to inevitably increase the cost of the control device.
Thus, an object of the invention is to provide a fuel cut control device for an internal combustion engine that detects a low load state of the internal combustion engine without using an expensive throttle sensor, and properly performs fuel cut control during deceleration of the internal combustion engine.
The invention is applied to a fuel cut control device for an internal combustion engine including a controller that performs fuel cut control to stop supply of fuel to the internal combustion engine during deceleration of a single-cylinder or multi-cylinder internal combustion engine having a throttle valve for each cylinder, or a multi-cylinder internal combustion engine having one throttle valve for two cylinders.
In the invention, xe2x80x9cmulti-cylinder internal combustion enginexe2x80x9d means an internal combustion engine having two or more cylinders.
In the invention, the controller is comprised so as to detect a maximum value of an intake pipe pressure during one combustion cycle of the internal combustion engine, start the fuel cut control when it is detected that the detected maximum value of the intake pipe pressure becomes less than a set fuel cut start determination value, and stop the fuel cut control when it is detected that the detected maximum value of the intake pipe pressure exceeds a fuel supply restart determination value set higher than the fuel cut start determination value to restart the supply of the fuel to the internal combustion engine.
The controller may includes: an intake pipe pressure maximum value detection unit that detects the maximum value of the intake pipe pressure during one combustion cycle of the internal combustion engine; a fuel cut/restart timing detection unit that detects a timing when the maximum value of the intake pipe pressure detected by the intake pipe pressure maximum value detection unit becomes less than the set fuel cut start determination value, as fuel cut control start timing when the fuel cut control is started, and detects a timing when the maximum value of the intake pipe pressure detected by the intake pipe pressure maximum value detection unit exceeds the fuel supply restart determination value set higher than the fuel cut start determination value, as fuel supply restart timing when the fuel cut control is stopped to restart the supply of the fuel to the internal combustion engine; and a fuel supply control unit that controls the supply of the fuel to the internal combustion engine so as to start the fuel cut control when the fuel cut/restart timing detection unit detects the fuel cut control start timing, and restart the supply of the fuel to the internal combustion engine when the fuel supply restart timing is detected.
In a single-cylinder or multi-cylinder four-cycle internal combustion engine having a throttle valve for each cylinder, a change in the maximum value of the intake pipe pressure that occurs during one combustion cycle reflects a load state of the engine, and thus if an appropriate fuel cut start determination value and an appropriate fuel supply restart determination value are set with respect to the maximum value of the intake pipe pressure that occurs during one combustion cycle, the intake pipe pressure becomes less than the fuel cut start determination value when the engine decelerates, and the intake pipe pressure reaches above the fuel supply restart determination value when a rotational speed of the engine decreases to the extent that the supply of the fuel needs to be restarted.
Therefore, the fuel cut start determination value and the fuel supply restart determination value are appropriately set, the fuel cut control is started at the timing when the maximum value of the intake pipe pressure becomes less than the fuel cut start determination value, and the supply of the fuel is restarted at the timing when the maximum value of the intake pipe pressure reaches above the fuel supply restart determination value, thereby allowing proper fuel cut control without detecting an opening degree of the throttle valve.
In a multi-cylinder four-cycle internal combustion engine having one throttle valve for two cylinders, the intake pipe pressure represents a maximum value immediately before one of the two cylinders enters a suction stroke, and the intake pipe pressure represents a minimum value before the suction stroke of one of the cylinders finishes.
Therefore, also in the multi-cylinder internal combustion engine having one throttle valve for two cylinders, the fuel cut start determination value and the fuel supply restart determination value are appropriately set, the fuel cut control is started at the timing when the maximum value of the intake pipe pressure becomes less than the fuel cut start determination value, and the supply of the fuel is restarted at the timing when the maximum value of the intake pipe pressure reaches above the fuel supply restart determination value, thereby allowing proper fuel cut control without detecting an opening degree of the throttle valve.
In the case where a vehicle drives on uplands, if the fuel cut start determination value and the fuel supply restart determination value are set to fixed values appropriate for lowland driving when the above described control is performed, a difference between the atmospheric pressure and the fuel cut start determination value decreases during highland driving to cause frequent fuel cut control leading to an unstable operation of the engine, since the atmospheric pressure is reduced on uplands. If the atmospheric pressure becomes equal to or lower than the fuel supply restart determination value, the supply of the fuel cannot be restarted, and the engine stalls.
In order to prevent such a problem, in a preferred aspect of the invention, the controller further includes: an atmospheric pressure measurement unit that measures atmospheric pressure or an atmospheric pressure estimation unit that estimates the atmospheric pressure from the intake pipe pressure; and determination value deciding means that decides the fuel cut start determination value and the fuel supply restart determination value depending on an atmospheric pressure value obtained by the atmospheric pressure measurement unit or the atmospheric pressure estimation unit.